Fluid catalyst regeneration process and apparatus

ABSTRACT

Methods of control and control systems for a catalyst regeneration process and apparatus for the oxidative removal of coke from a coke-contaminated fluid catalyst. Simultaneous production of hot regenerated catalyst and a relatively-cooler flue gas is provided. The process comprises a high temperature coke combustion zone, and a lower temperature heat removal zone. Coke contaminated catalyst, oxygen containing gas and regenerated catalyst from the heat removal zone are contacted in the high temperature combustion zone, the temperature of which is controlled by adjusting the rate at which catalyst is recycled from the heat removal zone. Catalyst maybe withdrawn from the top of the combustion zone and sent to the reaction zone at the controlled combustion zone temperature, the remainder of the catalyst and the hot flue gas pass to the upper heat removal zone, where both gas and catalyst are cooled, preferably by utilizing the catalyst as a heat transfer medium in a dense-phase heat exchange system. The optimum temperature may be achieved by mixing regenerated catalyst from the two zones, and 0-100% of regenerated catalyst may be withdrawn from either of the two zones. The extent of heat removal in the upper zone can be adjusted by changing the level of the dense bed in the heat removal zone, and this would be used for making gross changes in the quantity of the heat removed from the process.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of my prior, copendingapplication Ser. No. 969,607 filed Dec. 14, 1978 and issued as U.S. Pat.No. 4,219,442 on Aug. 26, 1980. All of the teachings of this priorapplication are incorporated herein by reference thereto.

BACKGROUND OF THE INVENTION

The field of art to which this invention pertains is fluid catalystregeneration. It relates to the rejuvenation of particulated-solid,fluidizable catalyst which has been contaminated by the depositionthereupon of coke. The present invention will be most useful in aprocess for regenerating coke-contaminated fluid cracking catalyst, butit should find use in any process in which coke is burned from a solid,particulated fluidizable catalyst.

DESCRIPTION OF THE PRIOR ART

The fluid catalytic cracking process (hereinafter FCC) has beenextensively relied upon for the conversion of starting materials, suchas vacuum gas oils, and other relatively heavy oils, into lighter andmore valuable products. FCC involves the contact in a reaction zone ofthe starting material, whether it be vacuum gas oil or another oil, witha finely divided, or particulated, solid, catalytic material whichbehaves as a fluid when mixed with a gas or vapor. This materialpossesses the ability to catalyze the cracking reaction, and in soacting it is surface-deposited with coke, a byproduct of the crackingreaction. Coke is comprised of hydrogen, carbon and other material suchas sulfur, and it interferes with the catalytic activity of FCCcatalysts. Facilities for the removal of coke from FCC catalyst,so-called regeneration facilities or regenerators, are ordinarilyprovided within an FCC unit. Regenerators contact the coke-contaminatedcatalyst with an oxygen-containing gas at conditions such that the cokeis oxidized and a considerable amount of heat is released. A portion ofthis heat escapes the regenerator with flue gas, comprised of excessregeneration gas and the gaseous products of coke oxidation, and thebalance of the heat leaves the regenerator with the regenerated, orrelatively coke-free, catalyst. Regenerators operating atsuperatmospheric pressures are often fitted with energy-recoveryturbines which expand the flue gas as it escapes from the regeneratorand recover a portion of the energy liberated in the expansion.

The fluidized catalyst is continuously circulated from the reaction zoneto the regeneration zone and then again to the reaction zone. The fluidcatalyst, as well as providing catalytic action, acts as a vehilce forthe transfer of heat from zone to zone. Catalyst exiting the reactionzone is spoken of as being "spent", that is partially deactivated by thedeposition of coke upon the catalyst. Catalyst from which coke has beensubstantially removed is spoken of as "regenerated catalyst".

The rate of conversion of the feed stock within the reaction zone iscontrolled by regulation of the temperature, activity of catalyst andquantity of catalyst (i.e. catalyst to oil ratio) therein. The mostcommon method of regulating the temperature is by regulating the rate ofcirculation of catalyst from the regeneration zone to the reaction zonewhich simultaneously increases the catalyst/oil ratio. That is to say,if it is desired to increase the conversion rate an increase in the rateof flow in circulating fluid catalyst from the regenerator to thereactor is effected. Inasmuch as the temperature within the regenerationzone under normal operations is invariably higher than the temperaturewithin the reaction zone, this increase in influx of catalyst from thehotter regeneration zone to the cooler reaction zone effects an increasein reaction zone temperature. It is interesting to note that: thishigher catalyst circulation rate is sustainable by virtue of the systembeing a closed circuit; and, the higher reactor temperature issustainable by virtue of the fact that increased reactor temperatures,once effected, produce an increase in the amount of coke being formed inthe reaction and deposited upon the catalyst. This increased productionof coke, which coke is deposited upon the fluid catalyst within thereactor, provides, upon its oxidation within the regenerator, anincreased evolution of heat. It is this increased heat evolved withinthe regeneration zone which, when conducted with the catalyst to thereaction zone, sustains the higher reactor temperature operation.

Recent, politico-economic restraints which have been put upon thetraditional lines of supply of crude oil have made necessary the use, asstarting materials in FCC units, of heavier-than-normal oils. FCC unitsmust now cope with feed stocks such as residual oils and in the futuremay require the use of mixtures of heavy oils with coal or shale derivedfeeds.

The chemical nature and molecular structure of the feed to the FCC unitwill affect that level of coke on spent catalyst. Generally speaking,the higher the molecular weight, the higher the Conradson carbon, thehigher the heptane insolubles, and the higher the carbon to hydrogenratio, the higher will be the coke level on the spent catalyst. Alsohigh levels of combined nitrogen, such as is found in shale derivedoils, will also increase the coke level on spent catalyst. Theprocessing of heavier and heavier feedstocks, and particularly theprocessing of deasphalted oils, or direct processing of atmosphericbottoms from a crude unit, commonly referred to as reduced crude, doescause an increase in all or some of these factors and does thereforecause an increase in coke level on spent catalyst.

This increase in coke on spent catalyst results in a larger amount ofcoke burnt in the regenerator per pound of catalyst circulated. Heat isremoved from the regenerator in conventional FCC units in the flue gasand principally in the hot regenerated catalyst stream. An increase inthe level of coke on spent catalyst will increase the temperaturedifference between the reactor and the regenerator, and in theregenerated catalyst temperature. A reduction in the amount of catalystcirculated is therefore necessary in order to maintain the same reactortemperature. However, this lower catalyst circulation rate required bythe higher temperature difference between the reactor and theregenerator will result in a fall in conversion, making it necessary tooperate with a higher reactor temperature in order to maintainconversion at the desired level. This will cause a change in yieldstructure which may or may not be desirable, depending on what productsare required from the process. Also there are limitations to thetemperatures that can be tolerated by FCC catalyst without there being asubstantial detrimental effect on catalyst activity. Generally, withcommonly available modern FCC catalyst, temperatures of regeneratedcatalyst are usually maintained below 1350° F., since loss of activitywould be very severe above 1400°-1450° F. Also, energy recoveryturbines, sometimes called "power recovery turbines", commonly cannottolerate flue gas at temperatures in excess of 1300°-1350° F. If arelatively common reduced crude such as that derived from Light Arabiancrude oil were charged to a conventional FCC unit, and operated at atemperature required for high conversion to lighter products, i.e.similar to that for a gas oil charge, the regenerator temperature wouldoperate in the range of 1600°-1800° F. This would be too high atemperature for the catalyst, require very expensive materials ofconstruction, and give an extremely low catalyst circulation rate. It istherefore accepted that when materials are processed that would giveexcessive regenerator temperatures, a means must be provided forremoving heat from the regenerator, which enables a lower regeneratortemperature, and a lower temperature difference between the reactor andthe regenerator.

Prior art methods of heat removal generally provide coolant-filled coilswithin the regenerator, which coils are in contact either with thecatalyst from which coke is being removed or with the flue gas justprior to the flue gas' exit from the regenerator. For example, McKinneyU.S. Pat. No. 3,990,992 discloses a fluid catalytic cracking processdual zone regenerator with cooling coils mounted in the second zone. Thesecond zone is for catalyst disengagement prior to passing the flue gasfrom the system, and contains catalyst in a dilute phase. Coolantflowing through the coils absorbs heat and removes it from theregenerator.

These prior art coils have been found to be inflexible in that they areusually sized to remove the quantity of heat which will be liberated bythe prospective feed stock which is most extensively coke-forming.Difficulties arise when a feed stock of lesser coke-formingcharacteristics is processed. In such a case the heat-removal coils arenow oversized for the job at hand. They, consequently, remove entirelytoo much heat. When heat removal from the regenerator is higher thanthat required for a particular operation, the temperature within theregenerator is depressed. This leads to a lower than desired temperatureof regenerated catalyst exiting the regenerator. The catalystcirculation rate required to obtain the desired reaction zonetemperature will increase, and may exceed the mechanical limitations ofthe equipment. The coke production rate will be higher than necessary onthis feedstock, and the lower temperature will result in less efficientcoke burning in the regeneration zone, with a greater amount of residualcoke on regenerated catalyst. Such are the operational difficultiescaused by prior art heat removal means due to their inflexibility.

Indeed, these prior art heat removal schemes also significantlycomplicate the start-up of prior art units. The presence of inflexibleheat removal coils within the coke-oxidizing section of the regeneratoroften drastically extends the time period required for raising theregenerator to its operational temperature level.

Like the basic concept of heat removal from FCC regenerators, the basicconcept of internal and external recycle of catalyst particles in FCCregenerators is not, per se, novel. Examples of such concepts are taughtin Gross et al U.S. Pat. No. 4,035,284, Pulak U.S. Pat. No. 3,953,175,Strother U.S. Pat. No. 3,898,050, Conner et al U.S. Pat. No. 3,893,812,Pulak U.S. Pat. No. 4,032,299, Pulak U.S. Pat. No. 4,033,728, and PulakU.S. Pat. No. 4,065,269. The catalyst recycle schemes taught by thesereferences, however, even when considered in the light of the prior artmethods of heat removal, as discussed above, do not and are not able toachieve the simultaneous provision of flue gas cool enough for powerrecovery, a close control of the temperatures of the various regeneratedcatalyst streams and the control of heat removal from the regenerator.

The regeneration process and apparatus which I hereby disclose offer theadvantages of an easier and quicker start-up, the maintenance of fluegas cool enough for power recovery, the provision of regeneratedcatalyst hot enough to maintain desired feed stock conversion rates inthe reaction zone with reasonable catalyst circulation rates, and facilecontrol of both the regenerated catalyst temperature and the extent ofheat removal from the regenerator. My invention involves the combinationof a combustion zone, a heat removal zone and paths provided for theinternal and/or external recycle of streams of catalysts individuallywithdrawn from the zones.

SUMMARY OF THE INVENTION

Accordingly, the objectives of my invention are to provide in a processfor regenerating a coke-contaminated fluid catalyst (1) methods ofcontrol and control systems which enable a close control of thetemperature in the upper part of the combustion zone by the control ofthe recirculation of regenerated catalyst from which heat has beenremoved to the combustion zone or by circulation catalyst from an upperportion of the combustion zone to a power position; (2) heat removalfrom the regenerator and close control thereof by manipulating theextent of immersion of heat removal means in a dense-phase fluid bed ofthe regenerator; (3) close control of the temperature of the regeneratedcatalyst required for circulation to the reactor by obtaining thecatalyst from either the heat removal zone of the regenerator, in whichit is relatively cool, or the combustion zone of the regenerator inwhich it is hottest, or as a mixture from both of these sources inrelative amounts selected to impart the desired temperature to themixture; and (4) close control of the temperature of thecoke-contaminated fluid catalyst at the point of introduction of thecatalyst into the combustion zone.

My invention, in a first embodiment, comprises a process forregenerating a coke-contaminated fluid catalyst to obtain a regeneratedcatalyst of a pre-determined temperature range with return of theregenerated catalyst to a hydrocarbon conversion zone. The processcomprises: (a) introducing oxygen containing regeneration gas andcoke-contaminated fluid catalyst into a lower locus of a relativelydilute phase combustion zone maintained at a temperature sufficient forcoke oxidation and therein oxidizing coke to produce hot regeneratedcatalyst and hot flue gas; (b) collecting and withdrawing from an upperlocus of its relatively dilute phase combustion zone a portion of thehot regenerated catalyst; (c) transporting the hot flue gas and theremaining portion of the hot regenerated catalyst into a lower locus ofa relatively dense phase heat removal zone and therein maintaining itscatalyst at relatively dense phase fluid bed conditions; (d) withdrawingheat by a heat removal means from its hot regenerated catalyst in therelatively dense phase heat removal zone, and (e) recovering regeneratedcatalyst possessing the pre-determined temperature range for its returnto the hydrocarbon conversion zone by (1) either withdrawing therequired regenerated catalyst exclusively from the upper locus of therelatively dilute phase combustion zone when the desired temperature ofthe regenerated catalyst is the upper limit of the pre-determined range;or (2) withdrawing a portion of the required regenerated catalyst fromthe relatively dense phase heat removal zone, withdrawing a portion fromthe upper locus of the relatively dilute phase combustion zone andthereafter admixing the withdrawn portions. The first embodimentincludes a method of control comprising sensing the temperature of theadmixture of regenerated catalyst and controllably withdrawing theregenerated catalyst from the relatively dense phase heat removal zoneresponsive to the temperature, thereby admixing the withdrawn portionsin suitable proportions for maintaining the temperature within thepre-determined temperature range.

My invention in a second embodiment comprises a process for regeneratinga coke-contaminated fluid catalyst to obtain a regenerated catalyst of apre-determined temperature range for return of the regenerated catalystto a hydrocarbon conversion zone which process comprises: (a)introducing oxygen containing gas and coke-contaminated fluid catalystinto a lower locus of a relatively dilute phase combustion zone maintainat a temperature sufficient for coke oxidation and therein oxidizingcoke to produce the hot regenerated catalyst and hot flue gas; (b)collecting the withdrawing from an upper locus of the relatively dilutephase combustion zone a portion of the hot regenerated catalyst; (c)transporting the hot flue gas and the remaining portion of the hotregenerated catalyst into a lower locus of a relatively dense phase heatremoval zone and therein maintaining the catalyst at relatively densephase fluid bed conditions; and (d) withdrawing heat by a heat removalmeans from the hot regenerated catalyst maintained in the relativelydense phase heat removal zone. The second embodiment includes a methodof controlling the temperature at the upper locus of the relativelydilute phase combustion zone comprising sensing the temperature at theupper locus and controllably withdrawing the regenerated catalyst fromthe relatively dense phase and introducing the withdrawn portion intothe lower locus of the relatively dilute phase combustion zoneresponsive to the temperature.

My invention in a third embodiment comprises a process for regeneratinga coke-contaminated fluid catalyst to obtain a regenerated catalyst of apre-determined temperature range for return of the regenerated catalystto a hydrocarbon conversion zone which process comprises: (a)introducing oxygen containing regenerated gas and coke-contaminatedfluid catalyst into a lower locus of a dilute phase combustion zonemaintained at a temperature sufficient for coke oxidation and thereinoxidizing coke to produce hot regenerated catalyst and hot flue gas; (b)collecting and withdrawing from an upper locus of the dilute phasecombustion zone a portion of the hot regenerated catalyst. The thirdembodiment includes a method of controlling the inlet temperature of thedilute phase combustion zone comprising sensing the temperature at theinlet and controllably returning a part of the regenerated catalystcollected and withdrawn from the upper locus of the dilute phasecombustion zone to a lower locus of the dilute phase combustion zoneresponsive to the temperature.

My invention in a fourth embodiment comprises a process for regeneratinga coke-contaminated fluid catalyst to obtain a regenerated catalyst of apre-determined temperature range for return of said regenerated catalystto a hydrocarbon conversion zone which process comprises: (a)introducing oxygen containing regeneration gas and coke-contaminatedfluid catalyst into a lower locus of a dilute phase combustion zonemaintained at a temperature sufficient for coke oxidation and thereinoxidizing coke to produce hot regenerated catalyst and hot flue gas; (b)collecting and withdrawing from an upper locus of the dilute phasecombustion zone a portion of the hot regenerated catalyst. The fourthembodiment includes a method of controlling the temperature of thecoke-contaminated fluid catalyst at the locus of the introduction of thecatalyst into the lower locus of the dilute phase combustion zonecomprising sensing the temperature and controllably mixing a part of theregenerated catalyst collected and withdrawn from the upper locus of thedilute phase combustion zone with the coke-contaminated fluid catalystat a locus upstream of the locus of introduction.

My invention in a fifth embodiment comprises an apparatus forregenerating a coke-contaminated, fluid catalyst which apparatuscomprises in combination: (a) a vertically oriented combustion chamber;(b) a spent catalyst inlet conduit for gas and fluid catalyst connectingwith the lower portion of the combustion chamber; (c) fluid catalystcollecting means disposed within an upper portion of the combustionchamber; (d) a first catalyst withdrawal conduit, connecting with thecatalyst collecting means, for withdrawal of collected regenerated fluidcatalysts from the combustion chamber; (e) a heat removal chamberlocated super adjacent to the combustion chamber and in communicationtherewith; (f) heat removal means disposed within the heat removalchamber; (g) a second catalyst withdrawal conduit connected at one endto the heat removal chamber for withdrawing regenerated fluid catalystfrom the heat removal chamber; and (h) a mixing conduit connected at oneend to the second withdrawal conduit and at the other end to the firstwithdrawal conduit, such that regenerated fluid catalyst from the heatremoval chamber can pass into the first withdrawal conduit. The fifthembodiment includes a control system for the apparatus comprising meansto sense the catalyst temperature in the first withdrawal conduit at alocus downstream of the locus where the mixing conduit connects to thefirst withdrawal conduit, temperature control means having an adjustableset point connecting with the temperature sensing means and developingan output signal, flow control means regulating the rate of flow ofregenerated catalyst through the mixing conduit, and means fortransmitting the output signal to the flow control means whereby thelatter is adjusted responsive to the catalyst temperature.

My invention in a sixth embodiment comprises an apparatus forregenerating a coke-contaminated, fluid catalyst, which apparatuscomprises in combination: (a) a vertically oriented combustion chamber;(b) a spent catalyst inlet conduit for gas and fluid catalyst connectingwith the lower portion of the combustion chamber; (c) a heat removalchamber located super adjacent to the combustion chamber and incommunication therewith; (d) heat removal means disposed within the heatremoval chamber; (e) a catalyst withdrawal conduit connected at one endto the heat removal chamber for withdrawing regenerated fluid catalystfrom the heat removal chamber; and (f) a catalyst recycle conduitconnecting the withdrawal conduit with the lower portion of thecombustion chamber, such that regenerated fluid catalyst can pass fromthe heat removal chamber to the combustion chamber. The sixth embodimentincludes a control system for the apparatus comprising means to sensethe catalyst temperature an upper locus of the combustion chamber,temperature control means having an adjustable set point connecting withthe temperature sensing means and developing an output signal, flowcontrol means regulating the rate of flow of regenerated catalystthrough the catalyst withdrawal conduit, and means for transmitting theoutput signal to the flow control means whereby the latter is adjustedresponsive to the catalyst temperature.

My invention in a seventh embodiment comprises an apparatus forregenerating a coke-contaminated, fluid catalyst which apparatuscomprises in combination: (a) a vertically oriented combustion chamber;(b) a spent catalyst inlet conduit for gas and fluid catalyst connectingwith the lower portion of the combustion chamber; (c) fluid catalystcollecting means disposed within an upper portion of the combustionchamber; and (d) a catalyst recycle conduit connecting with the catalystcollecting means at one end and discharging into the lower portion ofthe combustion chamber at the other end, such that fluid catalyst canpass from said upper portion of the combustion chamber to the lowerportion of the combustion chamber. The seventh embodiment includes acontrol system for the apparatus comprising means to sense the catalysttemperature at the lower portion of the combustion chamber, temperaturecontrol means having an adjustable set point connecting with thetemperature sensing means and developing an output signal, flow controlmeans regulating the rate of flow of regenerated catalyst through thecatalyst recycle conduit, and means for transmitting the output signalto the flow control means whereby the latter is adjusted responsive tothe catalyst temperature.

My invention in an eighth embodiment comprises an apparatus forregenerating a coke-contaminated, fluid catalyst which apparatuscomprises in combination: (a) a vertically oriented combustion chamber;(b) a spent catalyst inlet conduit for gas and fluid catalyst connectingwith the lower portion of the combustion chamber; (c) fluid catalystcollecting means disposed within an upper portion of the combustionchamber; (d) a catalyst withdrawal conduit connecting with the catalystcollecting means, for withdrawal of collected regenerated fluid catalystfrom the combustion chamber; and (e) a mixing conduit connected at oneend with the catalyst withdrawal conduit and at the other end with thespent catalyst inlet conduit. The eighth embodiment includes a controlsystem for the apparatus comprising means to sense the catalysttemperature at a lower portion of the combustion chamber, temperaturecontrol means having an adjustable set point connecting with thetemperature sensing means and developing an output signal, flow controlmeans regulating the rate of flow of regenerated catalyst through themixing conduit, and means for transmitting the output signal to the flowcontrol means whereby the latter is adjusted responsive to the catalysttemperature.

Other embodiments and objects of the present invention encompass furtherdetails such as process streams, the function and arrangement of variouscomponents of my apparatus, and control methods and systems relating tothe extent of immersion of the heat removal means in the dense phasefluid bed, all of which are hereinafter disclosed in the followingdiscussion of each of these facets of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional, elevation view of a regeneration apparatusaccording to the present invention, showing combustion zone 1 and heatremoval zone 2, recycle conduit 18, 20 and mixing conduit 33.

FIG. 2 is an enlarged sectional view of combustion zone 1, fluidcatalyst collecting means 8 and second mixing conduit 26'.

FIG. 3 is another enlarged, sectional view of combustion zone 1, showingsecond recycle conduit 29, 31.

Referring now to FIG. 1, a regenerator is shown which includesvertically-oriented combustion zone 1 in association with heat removalzone 2. Coke-contaminated catalyst enters the regenerator throughconduit 4, after having passed through flow control valve 5.Regeneration gas enters the system in conduit 3 and combines withcoke-contaminated catalyst in conduit 4 and regenerated catalyst inconduit 20 before passing to distributor 6 located in the lower part ofcombustion zone 1. The combination of conduits 20, 3 and 4 anddistributor 6 are referred to herein as "inlet for gas and catalyst".

A mixture of regeneration gas, regenerated catalyst andcoke-contaminated catalyst exit distributor 6 and pass upwardly withincombustion zone 1. Conditions within the combustion zone are such thatthe regeneration gas and coke combine chemically to form flue gas,leaving the catalyst relatively free from coke.

Fluid catalyst collecting means 8 is situated in an upper part ofcombustion zone 1 and in the proximity of surface 7 and passageway 11. Aportion of regenerated catalyst within the combustion zone is collectedby fluid catalyst collecting means 8 and exits the combustion zonethrough withdrawal conduit 9 and control valve 10. Any catalystcollected in means 8, in excess of that withdrawn through conduit 9,will overflow back into the combustion zone and be re-entrained by thecombustion gas. The remaining portion of regenerated catalyst withincombustion zone with flue gas through passageway 11 and impinges upondeflector 12, which serves to distribute the flue gas to the dense-phasefluidized bed in the heat removal zone.

Heat removal zone 2 is located above combustion zone 1 and communicatestherewith through passageway 11. Situated within heat removal zone 2are: heat removal means 21; means 14, 15 for withdrawing fluid catalyst;collecting means 17 and recycle conduit 18, 20; dense-phase fluidcatalyst bed 13; and gas-catalyst separation means 23. Pressuresensitive devices 35 and 37 connect with level sensing, recording andcontrol device 34 by way of lines 36 and 38, respectively. Level sensingand control device 34 connects to flow control valve 5 by way of line39. Temperature recorder control device 42 connects to temperaturesensing device 40 by way of line 41, and connects to control valve 19 byway of line 43. Temperature recorder control device 44 connects totemperature sensing device 47 by way of line 45, and connects to controlvalve 32 by way of line 46.

Flue gas and regenerated catalyst, having entered heat removal zone 2through passageway 11, intermingle with particulated catalyst indense-phase fluid bed 13. Means 14, 15 withdrawing fluid catalyst havingassociated with them flow control valve 16 for the control of the rateof catalyst withdrawal. The surface level of fluid bed 13 may be raisedor lowered indirectly by reducing or increasing the flow, respectively,through flow control valve 5. Level sensing, recording and controldevice 34 determines the level of the dense-phase catalyst bed 13 basedon the differentials in pressures measured by pressure sensitive devices35 and 37. Variations in bed density and/or depth of bed within thedense-phase region will be reflected in a varying pressure differential.Device 34 will then maintain a predetermined level in dense-phase bed 13by controlling control valve 5. Raising or lowering the level of fluidbed 13 increases or decreases, respectively, the extent of immersion ofheat removal means 21 in bed 13. Flue gas exits bed 13, entrainingtherewith a small amount of regenerated catalyst, and enters inlet 22 ofseparation means 23 where the entrained catalyst is disengaged from theflue gas. Flue gas, now separated from the priorly entrained catalyst,exits heat removal zone 2 through outlet 24. Priorly-entrained catalystreturns to fluid bed 13 from separation means 23 in conduits 25 and 26.

Recycle conduit 18, fitted with control valve 19, is provided in orderthat a flow of catalyst from dense-phase fluid bed 13 to regenerationgas inlet 3 may be established and regulated. Temperature recordercontrol device 42 determines the temperature of the catalyst in conduit9 and controls control valve 19 in response thereto so as to achieve apre-determined temperature setting.

Mixing conduit 33 is provided for communication between conduit 15 andconduit 9, such that catalyst withdrawn from heat removal zone 2 inconduit 15 may pass, through control valve 32, into conduit 9 downstreamof control valve 10. Temperature recorder control device 44 determinesthe temperature of the catalyst in conduit 9 and controls control valve32 in response thereto so as to achieve a predetermined temperaturesetting.

Turning now to FIG. 2, second mixing conduit 26', 28 and control valve27 are shown. This second mixing conduit is provided to accommodate aflow of regenerated catalyst from withdrawal conduit 9 tocoke-contaminated catalyst conduit 4. Temperature recorder controldevice 52 connects to temperature sensing device 50 by way of line 51,and connects to control valve 27 by way of line 53.

Proceeding to FIG. 3, the alternative recycle conduit 29, 31, having afixed flow regulating means 30, is indicated. The alternative recycleconduit is provided to furnish a flow path for regenerated catalyst fromfluid catalyst collecting means 8, internally with combustion zone 1, toa lower part of the combustion zone. Temperature recorder control device56 connects to temperature sensing device 54 by way of line 55, andconnects to flow regulating means 30 by way of line 57.

The above-described drawings are intended to be schematicallyillustrative of my invention and not be limitations thereon.

DETAILED DESCRIPTION OF THE INVENTION

The present invention, in its process aspects, consists of steps for theregenerative combustion within a combustion zone of thecoke-contaminated catalyst from a reaction zone to form hot flue gas andhot regenerated catalyst, collection and withdrawal of a portion of thehot regenerated catalyst, cooling of another portion of the hotregenerated catalyst within a heat removal zone, cooling of hot flue gaswithin the heat removal zone, using the cooled regenerated catalyst as aheat sink, and the use of portions of hot regenerated catalyst andcooled regenerated catalyst for control of the temperatures of thecombustion zone and the regenerated catalyst stream to be returned tothe reaction zone.

Reference will now be made to the attached drawings for a discussion ofthe regeneration process and apparatus of my invention. In FIG. 1regeneration gas, which may be air or another oxygen-containing gas,enters in conduit 3 and mixes with coke-contaminated catalyst enteringin conduit 4 and regenerated catalyst in conduit 20. The resultantmixture of coke-contaminated catalyst, regenerated catalyst andregeneration gas are distributed into the interior of combustion zone 1,at a lower locus thereof, by distributor 6. Coke-contaminated catalystcommonly contains 0.1 to 5 wt. % carbon, as coke. Coke is predominantlycomprised of carbon, however, it can contain from 5 to 15 wt. %hydrogen, as well as sulfur and other materials. The regeneration gasand entrained catalyst flows upward from the lower part of combustionzone 1 to the upper part thereof. While it is not critical to thepractice of this invention, it is believed that dilute phase conditions,that is a catalyst/gas mixture of less than 30 lbs. per cubic foot, andtypically 2-10 lbs. per cubic foot, are the most efficient for cokeoxidation. At the catalyst/gas mixture ascends within combustion zone 1the heat of combustion of coke is liberated and absorbed by the nowrelatively carbon-free catalyst, in other words by the regeneratedcatalyst.

The rising catalyst/gas stream impinges upon surface 7, whichimpingement charges the direction of flow of the steam. It is well knownin the art that impingement of a fluidized particulate stream upon asurface, causing the stream to turn through some angle, can result inthe separation from the stream of a portion of the solid materialtherein. The impingement of the catalyst-gas stream upon surface 7within combustion zone 1 causes a portion of the hot regeneratedcatalyst flowing in the combustion zone to collect within fluid catalystcollecting means 8. Means 8 may be a cone-shaped receptacle, as shown,or any other shape appropriate for collecting catalyst particles. Thegaseous products of coke oxidation and excess regeneration gas, or fluegas, and the uncollected portion of hot regenerated catalyst flowthrough passageway 11 and enter fluidized bed 13 within super adjacentheat removal zone 2. The density of the catalyst-gas mixture within bed13 is preferably maintained at 30 lbs. per cubic foot or higher and itis therefore characterized as a dense-phase fluid bed.

I prefer the maintenance of a dense-phase fluid bed within the heatremoval zone, rather than a dilute-phase fluid bed, because dense-phaseconditions afford greatly increased heat transfer rates from the bed toheat removal means 21. Heat removal means 21 are provided to withdrawheat from the dense-phase bed. In a preferred embodiment of my inventionthe heat removal means comprise conduits of substantially verticalorientation, the interiors of which conduits are sealed from theinterior of the heat removal zone, and which conduits having flowingtherein a heat-absorbing material, such as water. The objective is toabsorb heat into the heat-absorbing material through its indirectcontact with dense-phase fluid bed 13. As the heat transfer coefficientis much higher for the section of the tubes immersed in the fluidizedbed, than for the section of tubes above the bed, changing the extent ofimmersion will change the amount of heat removed. The immersion of heatremoval means 21 may be varied by any suitable means, including thevertical displacement of the heat removal means with respect to thedense-phase bed or the variation in regenerated catalyst inventorywithin the heat removal zone. In this embodiment the surface of fluidbed 13, and therefore the extent of immersion of heat removal means 21,is controlled through the action of control valve 5, and the resultingfluctuations of the catalyst level in the reactor or reactor catalyststripper are permitted. However, when widely different feedstocks areprocessed, producing widely different amounts of coke, and as a resultrequiring widely different heat removal from the regenerator, it isforeseen that additional catalyst would be added to the unit in order toallow a substantial increase in the level of bed 13, without losing thecatalyst level entirely in the associated reactor or reactor catalyststripper. It should also be understood that it will not be necessary tomake changes in the catalyst inventory of the heat removal zone toaccommodate relatively small changes in the coke level on spentcatalyst, as would be encountered when changing between two relativelysimilar reduced crude feeds, or as might be caused by some change inoperating conditions within the reactor section, or slight change infeed charge rate to the reactor section. If small changes in coke onspent catalyst or heat removal requirement occur, it is anticipated thatthe operating temperature in the heat removal zone would be allowed tovary over a range of say 50° F. before any adjustments of level isrequired, and this change in temperature would automatically adjust theamount of heat removed. Although the temperature in the heat removalzone may vary over a range of say 50° F., the temperature at the top ofthe combustor, and of the catalyst withdrawn through collection means 8will remain unchanged and steady at the selected control temperature.This provides a degree of freedom not previously available to the FCCoperator.

Control of the extent of immersion of the heat removal means in thedense-phase fluid bed of the heat removal zone is effected by levelcontrol means 34, which has a set point that may be manually adjusted,thereby manipulating the extent of immersion of the heat removal meansin the dense-phase responsive to the temperature thereof. The levelcontrol means controls the extent of immersion of the heat removal meansby sensing the extent of immersion with level sensing means 35 and 37which connect to level control means 34 via lines 36 and 38, generatinga level output signal from level control means 34, and transmitting thelatter via line 39 to contaminated catalyst flow control means 39whereby the latter is adjusted responsive to the extent of immersion.

Hot regenerated catalyst within the heat removal zone contacts, and iscooled by, heat removal means 21. The cooled regenerated catalystthereafter contacts hot flue gas which is ascending through the fluidbed within the heat removal zone. This contact results in heat exchangebetween the hot flue gas and the cooler regenerated catalyst, providinga relatively cooler flue gas. The relatively cooler flue gas exits fluidbed 13 and enters separation means 23 through inlet 22. These separationmeans may be cyclone separators, as schematically shown in FIG. 1, orany other effective means for the separation of particulated catalystfrom a gas stream. Catalyst separated from the relatively cooler fluegas returns to dense-phase fluid bed 13 through conduits 25 and 26. Therelatively cooler flue gas exits heat removal zone 2 via conduit 24,through which it may safely proceed to associated energy recoverysystems.

Recycle conduit 18 is attached at one end to a lower part of the heatremoval zone and at the other end to a lower part of the combustionzone. Cooler regenerated catalyst proceeds through this conduit, theflow rate being controlled by control valve 19, from heat removal zone 2to combustion zone 1 and provides a heat sink for the reduction andthereby a control of the combustion zone temperature. The flow rate ofthe cooler regenerated catalyst stream will be controlled in order tomaintain a constant temperature of the catalyst withdrawn from conduit9, or alternatively, the temperature of the mixture of flue gas andcatalyst passing through passageway 11. These temperatures will commonlybe in the range of 1300°-1400° F.

Control of the temperature of the regenerated catalyst at the upperlocus of the combustion zone is effected by sensing that temperaturewith sensing means 40, connecting the latter via line 41 to temperaturecontrol means 42 which has an adjustable set and which develops anoutput signal, transmitting the latter via line 43 to flow control means19, and adjusting the latter responsive to the upper locus temperature,thereby controllably withdrawing the catalyst from the heat removal andpassing it to a lower locus of the combustion zone.

Means 14 may be provided within heat removal zone 2 for the withdrawalof cooler regenerated catalyst therefrom.

As aforesaid, the hot regenerated catalyst in conduit 9 is returned tothe reaction zone at a rate sufficient to sustain the requiredtemperature within the reaction zone. It is highly desirable, therefore,that the hot regenerated catalyst temperature be controllable at anoptimum level. Operating in accordance with this invention it ispossible to select catalyst at the temperature of the combustion zone,through collection means 8, or of the heat removal zone throughcollection means 14. If neither of these temperatures are optimum forthe reaction section, then a controlled temperature intermediate betweenthese two can be achieved by utilizing conduit 33 and associated controlvalve 32. Conduit 33 which is connected at one end to the means forwithdrawing cooler regenerated catalyst from heat removal zone 2 and atthe other end to the conduit for withdrawal of hot regenerated catalyst9, is a mixing conduit as it provides a path for the introduction ofcooler regenerated catalyst into the hot regenerated catalyst stream forthe purpose of lowering the temperature of the hot regenerated catalyststream when necessary to maintain the temperature of the stream ofregenerated catalyst returning to the reaction zone. This will permitblending of catalyst from the regeneration and heat removal zones, inorder to obtain a catalyst stream for return to the reactor at atemperature intermediate between the temperature of regeneration andheat removal zones. This mode of operation is suggested as analternative to the other options of withdrawing 100% of the catalystfrom either of the two zones, or of having separate inlets to thereactor riser for the regenerated catalyst from each zone.

Control of the desired temperature of the catalyst blend is effected bysensing the temperature of the catalyst blend with temperature sensingmeans 47, connecting the latter via line 45 to temperature control means44 which has an adjustable set point and which develops an outputsignal, transmitting the latter via line 46 to flow control means 32,and adjusting the latter responsive to the blend temperature, therebycontrollably withdrawing the catalyst from the heat removal zone forblending with catalyst from the regeneration zone responsive to theblend temperature.

Reiterating, it is often desirable that the temperature within thecombustion zone be amenable to control at a preselected, constant level.Conduit 18 has been provided for the introduction to combustion zone 1of cooler regenerated catalyst in order to suppress and control thetemperature within the combustion zone.

It may also be desirable to provide an affirmative method for minimizingthe temperature rise across the combustion zone. This will result in alower temperature rise across the regeneration zone, and the higheraverage combustion temperature could be used in order to obtain greaterregeneration efficiency. FIG. 2 indicates the provision of second mixingconduit 26', 28 and associated flow control valve 27. This second mixingconduit provides for the recycle of hot regenerated catalyst, a part ofthat collected in the upper locus of the combustion zone by collectingmeans 8, to a lower locus of the combustion zone. Such recycle of hotregenerated catalyst to the relatively cooler, lower region of thecombustion zone provides a heat input which raises the temperature ofthe lower region of the combustion zone.

Control of the lower combustion zone temperature may be effected bysensing that temperature with sensing means 50, connecting the lattervia line 53 to temperature control means 52 which has an adjustable setpoint and which develops an output signal, transmitting the latter vialine 53 to flow control means 27, and adjusting the latter responsive tothe lower locus temperature, thereby controllably recycling hotregenerated catalyst collected in the upper locus by collecting means 8to the lower locus of the combustion zone via conduits 9, 26', 28, 4 and3, and via flow control means 27.

Another manner of effecting a minimum temperature rise across thecombustion zone and an increased lower combustion zone temperature isshown in FIG. 3. Hot regenerated catalyst which has been collected bymeans 8 at a relatively hotter, upper locus of the combustion zone maybe returned directly to a relatively cooler lower locus of thecombustion zone to raise the temperature therein. FIG. 3 indicates asecond recycle conduit, designated as item 29, 31. The second recycleconduit is connected at one end to fluid catalyst collecting means 8,and the other end is in open communication with a lower locus of thecombustion zone. Also shown in FIG. 3 is flow restricting means 30situated in the second recycle conduit. Such a flow restricting deviceis desirable for the purpose of controlling the extent of increase ofcombustion zone temperature by control of the rate of internal recycleof hot regenerated catalyst through the second recycle conduit. Item 30may be a flow control valve, a restriction orifice, or any otherappropriate flow-varying means.

Control of the lower combustion zone temperature is effected by sensingthat temperature with sensing means 54, connecting the latter via line55 to temperature control means 56 which has an adjustable set point andwhich develops an output signal, transmitting the latter via line 57 toflow control means 30, and adjusting the latter responsive to the lowerlocus temperature, thereby controllably withdrawing the catalyst fromcollecting means 8 and passing it to the lower locus of the combustionzone.

ILLUSTRATIVE EMBODIMENT

The following example represents a particularly preferred modecontemplated for the practice of my invention, expressed in terms of themass flow rates and temperatures of streams flowing in the regeneratordepicted in attached FIG. 1. The regenerator processes spent catalystfrom a reaction zone which is cracking a reduced crude oil feed stock.In the tabulation below the streams flowing within conduits aretabulated in registry with the item numbers of the conduits shown inFIG. 1.

    ______________________________________                                        Stream                       lbs./hr. °F.                              ______________________________________                                         4    Coke Contaminated Catalyst (from                                                                     2,724,552                                                                              1050                                          reactor)                                                                      Catalyst               2,691,362                                                                              1050                                          Coke                     30,902 1050                                     3    Regeneration Gas (air)   463,530                                                                               307                                     9    Hot Regenerated Catalyst From Upper                                           Locus of Combustion Zone (to reactor)                                                                2,691,362                                                                              1380                                    11    Hot Regenerated Catalyst plus                                                 Hot Flue Gas           4,114,730                                                                              1400                                          Hot Catalyst           3,621,428                                                                              1400                                          Hot Gas                  493,302                                                                              1400                                    18,20 Recycled Cooler Regenerated Catalyst                                          (to inlet of combustion zone)                                                                        3,621,428                                                                              1230                                    24    Flue Gas                 493,302                                                                              1250                                    21    Heat Removed by Heat Removal Means - 169.17 ×                           10.sup.6 BTU/hr.                                                              Heat Losses From Regenerator Vessel - 3.41 ×                            10.sup.6 BTU/hr.                                                        ______________________________________                                    

It should be noted that in this particular operation the feed stock tothe reaction zone is a reduced crude oil, material which yields arelatively high coke production. Such a high coke production, and theconsequent, extraordinary high evolution of heat in the combustion zonemade necessary the recycle of 3,621,428 lbs./hr. of cooler regeneratedcatalyst from the heat removal zone to the combustion zone in order tolimit the maximum combustion zone temperature to 1400° F.

It should also be noted that this illustrative embodiment is presentedfor a system where all of the catalyst returned to the riser iswithdrawn from collection means 8 at 1380° F. If required, the catalystcould be withdrawn from the heat removal zone at 1230° F. This wouldresult in a substantial increase in the catalyst circulation rate to thereactor section in order to maintain the 1050° F. reaction zone shown.Furthermore, both the temperature at the top of the combustion zone andin the heat removal zone could be adjusted over a range of 100°-150° F.from the temperatures shown, by appropriate changes in heat removalsurface in the heat removal zone and circulation rates of the variousstreams shown.

No flow in conduits 26 or 29 has been shown in the illustrativeembodiment as these serve only to reduce the temperature rise across thecombustion zone and do not influence the overall heat balance of theregeneration system.

As shown in the data tabulation the hot regenerated catalyst iswithdrawn from the combustion zone at 1380° F., while the flue gas exitsthe heat removal zone at 1250° F., relatively cooler than the hotregenerated catalyst and well below the precautionary 1300° F. limit setby downstream energy recovery systems.

I claim as my invention:
 1. In a process for regenerating acoke-contaminated fluid catalyst to obtain a regenerated catalyst of apre-determined temperature range with return of said regeneratedcatalyst to a hydrocarbon conversion zone which process comprises:(a)introducing oxygen containing regeneration gas and coke-contaminatedfluid catalyst into a lower locus of a relatively dilute phasecombustion zone maintained at a temperature sufficient for cokeoxidation and therein oxidizing coke to produce hot regenerated catalystand hot flue gas; (b) collecting and withdrawing from an upper locus ofsaid relatively dilute phase combustion zone a portion of said hotregenerated catalyst; (c) transporting said hot flue gas and theremaining portion of said hot regenerated catalyst into a lower locus ofa relatively dense phase heat removal zone and therein maintaining saidcatalyst at relatively dense phase fluid bed conditions; (d) withdrawingheat by a heat removal means from said hot regenerated catalyst in saidrelatively dense phase heat removal zone; and (e) recovering regeneratedcatalyst possessing the predetermined temperature range for its returnto said hydrocarbon conversion zone by (1) either withdrawing therequired regenerated catalyst exclusively from said upper locus of saidrelatively dilute phase combustion zone when the desired temperature ofsaid regenerated catalyst is the upper limit of said pre-determinedrange; or (2) withdrawing a portion of the required regenerated catalystfrom said relatively dense phase heat removal zone, withdrawing aportion from said upper locus of said relatively dilute phase combustionzone and thereafter admixing said withdrawn portions, wherein saidwithdrawing is controlled by sensing the temperature of said admixtureof regenerated catalyst and controllably withdrawing said regeneratedcatalyst from said relatively dense phase heat removal zone responsiveto said temperature, thereby admixing said withdrawn portions insuitable proportions for maintaining said temperature within saidpre-determined temperature range.
 2. In the process of claim 1 whereinthe amount of heat removal in said relatively dense phase heat removalzone is manipulated by:(a) providing heat removal means partiallyimmersed in said dense phase fluid bed of said heat removal zone; and(b) manipulating the extent of immersion of said heat removal means insaid dense phase fluid bed, wherein said manipulation is controlled bysensing said extent of immersion and controllably manipulating the rateof introduction of said coke-contaminated fluid catalyst into said lowerlocus of said relatively dilute phase combustion zone responsive to saidextent of immersion.
 3. In a process for regenerating acoke-contaminated fluid catalyst to obtain a regenerated catalyst of apre-determined temperature range for return of said regenerated catalystto a hydrocarbon conversion zone which process comprises:(a) introducingoxygen containing gas and coke-contaminated fluid catalyst into a lowerlocus of a relatively dilute phase combustion zone maintained at atemperature sufficient for coke oxidation and therein oxidizing coke toproduce said hot regenerated catalyst and hot flue gas; (b) collectingand withdrawing from an upper locus of said relatively dilute phasecombustion zone a portion of said hot regenerated catalyst; (c)transporting said hot flue gas and the remaining portion of said hotregenerated catalyst into a lower locus of a relatively dense phase heatremoval zone and therein maintaining said catalyst at relatively densephase fluid bed conditions; and (d) withdrawing heat by a heat removalmeans from said hot regenerated catalyst maintained in said relativelydense phase heat removal zone; wherein said withdrawing of catalyst andsaid temperature at said upper locus of said relatively dilute phasecombustion zone is controlled by sensing said temperature at said upperlocus, controllably withdrawing said regenerated catalyst from saidrelatively dense phase and introducing said withdrawn portion into saidlower locus of said relatively dilute phase combustion zone responsiveto said temperature.
 4. In the process of claim 3 wherein the amount ofheat removal in said relatively dense phase heat removal zone ismanipulated by:(a) providing heat removal means partially immersed insaid dense phase fluid bed of said heat removal zone; and (b)manipulating the extent of immersion of said heat removal means in saiddense phase fluid bed, wherein said manipulation is controlled bysensing said extent of immersion and controllably manipulating the rateof said coke-contaminated fluid catalyst into said lower locus ofintroduction of said relatively dilute combustion zone responsive tosaid extent of immersion.